1. Field of the Invention
The present invention relates to a charging and discharging system, and more particularly, to a charging and discharging system of a vehicle power storage device.
2. Description of the Prior Art
With the advancement of technology and rise of environmental consciousness, improvement of power consumption of a vehicle has become an essential objective in the field. In addition to considering using vehicles with various reachable power sources, such as electric bicycles, electric motorcycles, and hybrid cars, improving the engine efficiency or adopting idling stop technology in the vehicles has also become an aim of research for enhancing the power consumption efficiency of the vehicles.
However, with the development of various power saving vehicles, control of a vehicle is getting more complicated. A variety of specifications based on the voltage and current of the interface between the vehicle systems and the power storage devices are established. Different types of power storage devices come with different characteristics of voltage and current on their own, which makes it an important issue to figure out and design a corresponding interface between a specific vehicle system and a dedicated power storage device.
It is well known that lead-acid batteries generate instantaneous large current when activated, which has essential impact on the life of the batteries. It is much harmful for the life of the conventional lead-acid batteries with the increasing number of times to be activated when installed on vehicles since the control system on-board is improved and the concept of power saving is flourishing. Although other types of power storage devices, such as a lithium ion battery, have shown improvement to handle the battery aging issue, power storage devices of the lithium ion type are much vulnerable to the voltage issue and some additionally challenges emerge when lithium ion batteries of different specifications are implemented on the current vehicle.
For example, a charging voltage of a conventional lead-acid battery used in a motorcycle is about 14.5 volts, while a full charged voltage of a single cell of LiNiMnCo battery is about 4.2 volts. Problems show up if the LiNiMnCo battery is to be disposed on the motorcycle, which is originally designed for receiving a lead-acid battery. To put it more particularly, the voltage of three sets of the LiNiMnCo batteries in series connection is about 12.6 volts when fully charged. In this configuration, the charging voltage, 14.5 volts, designed for a system of the lead-acid battery will cause the LiNiMnCo batteries in series connection overvoltage-charged, bringing about safety and aging issue. If 4 sets of LiNiMnCo batteries in series connection are implemented in the motorcycle, the full charged voltage of the batteries is about 16.8 volts. Although a system using 4 sets of LiNiMnCo batteries in series connection may not face the safety issue due to the overvoltage charge in this configuration, each LiNiMnCo battery can be charged only to 3.6 volts, which leads to constant power shortage.
The problems mentioned above happen not only in applications that the lead-acid batteries are to be replaced by the lithium-ion batteries, but also in applications when replacements between various power storage devices and various vehicles systems are carried out. A vehicle system is made supportive for one type of power storage device usually means the vehicle system may not support another type of power storage device since different power storage devices usually have different characteristics of voltage and current. Therefore, it is an important issue to put an effort on making an adaptive conversion between various power storage devices and various vehicle systems so as to provide more flexibility for the power storage devices to be applied on various vehicle systems.